The present invention relates generally to a method of processing soy flour. More particularly, the present invention relates to a method of processing soy flour to reduce the off-flavor.
Soybean flour or soy flour is a nutritious, high protein ingredient used in numerous food formulations. Soy flour is generally the flour produced by milling the whole, dehulled soybean. Flour or meal is made from fat extracted soybeans by numerous well-known means. Defatted flour or soybean concentrate is commonly used to make texturized soy product by extrusion processes. Soy protein isolates are produced by fractionating soy flour or concentrate to obtain functionality and other desirable attributes.
All soy products suffer from a beany flavor claimed to be the primary result of lipases and lipoxygenase (Lusas, Oil Seeds and Oil-bearing Materials, Chpt. 11, p.297, Handbook of Cereal Science and Technology, 2000) or a component of the carbohydrate fraction (Swartz, U.S. Pat. No. 4,556,069). Lipase and lipoxygenase produces a range of rancid flavors through action on the fat in the soy flour or concentrate.
The primary method for removal of lipase/lipoxygenase is to thermally inactivate the enzyme. This is commonly done in the fat extraction process using cracked or coarse pieces of the soybeans. Flour is not employed. Clatfelter, U.S. Pat. No. 4,209,541, used a unhulled, whole soybeans in a process that steamed then heat treated the whole bean in hot air followed by cracking and dehulling. A flour was then made under modified atmosphere (nitrogen) to pulverize the material into flour.
To remove flavors, generally, flour is made into an aqueous slurry and treated to reduce off-flavors. Alternatively, the flour is defatted and presented as a flake (Johnson, U.S. Pat. No. 5,936,069) or texturized by an extrusion or other cook process and then treated to remove beany or off-flavors. In slurry form, the slurry is cooked under pressure (Hildebolt, U.S. Pat. No. 4,168,657; Melcer et al., U.S. Pat. No. 4,054,679; Hildebolt et al., U.S. Pat. No. 4,038,432; Hildebolt, U.S. Pat. No. 4,038,431) or extruded with steam injection during (Hildebolt, U.S. Pat. No. 4,128,051) or treated post-extrusion by thermal process (Small, U.S. Pat. No. 4,245,552).
Alternatively, de-flavoring can be done by hydrating or making a slurry then centrifuging (spinning) the protein out as a fibrous material, separating it from the fluid (Hildebolt, U.S. Pat. Nos. 4,226,576 and 4,062,987). Steam is used to heat the slurry in U.S. Pat. No. 4,226,576 by a common device known as a jet-cooker to achieve temperatures in excess of 300xc2x0 F. Use of a hydrocyclone is taught in Armstrong, U.S. Pat. No. 4,146,534 to wash the protein, separating it from debris material. Ultrafiltration can also be employed in removal of flavor components (Goodnight Jr. et al., U.S. Pat. Nos. 3,995,071 and 4,091,120).
Alternatively, soy flour (including texturized soy flour) can be deflavored using masking properties of yeast for meat applications (Swartz, U.S. Pat. No. 4,556,571) or reacted with ammonia gas (Ridgway, U.S. Pat. No. 4,291,063) or using a solvent system (Youngquist, U.S. Pat. No. 3,998,800). Schmidt, U.S. Pat. No. 5,275,833 used hydration and bleaching agents to improve flavor.
As discussed above, thermal processing is generally recognized as means of removing the beany flavor in soy flours, however, the processes usually involve forming a slurry, pressure cooking and venting the volatile compounds. Kijima, U.S. Pat. No. 4,125,465 uses a process specific for texturized soy products in which superheated steam flows through a vessel in a fluidized manner. Other patents utilize slurries or even doughs that are then extruded into sheets or doughs and baked (Wilding, U.S. Pat. No. 4,044,157).
We discovered a process that will treat conventional, whole soybean flourxe2x80x94enzyme activexe2x80x94without forming a slurry, at atmospheric pressure and in a manner extremely conducive for ingredient use in a wide variety of products.
The present invention is a method of processing soy flour to reduce the off-flavor. Soy flour processed according to the present invention has substantially no off-flavor while retaining substantially all of the functionality typically present in unprocessed soy flour.
In spite of the numerous nutritional benefits of soy flour, the potential applications in which soy flour may be used are limited by the off-flavor typically present in soy flour. Because soy flour processed according to the present invention eliminates the off-flavors, the soy flour may be used in a broader range of applications than was possible with conventional soy flour.
Whole, full fat, soybean flour commonly available as an xe2x80x9cenzyme activexe2x80x9d product of common grind (U.S. 90 mesh) or finer grind (500 to 1000 mesh) is fed into a reactor. The reactor includes a paddle assembly rotatably mounted therein. The reactor also preferably includes a jacket to control the temperature of the reactor. The reactor further preferably has the capability to inject steam into the interior of the reactor. A preferred embodiment of the reactor is described in Pikus et al., U.S. Pat. No. 5,271,163, the disclosure of which is incorporated herein by reference.
The reactor forms a thin film of material around the reactor cylinder that permits rapid heat transfer from the jacket wall and enables steam to be injected into the flour via injectors in the paddles. Water is optional since steam is injected. However, low amounts water may be added immediately after the solids feed port via a nozzle. The concentration of water added to the reactor is less than 10 percent by weight of the feed and preferably less than about 5 percent by weight of the feed.
The jacket temperature is preferably operated at between about 270 and 280xc2x0 F. to aid in vaporizing the off-flavors. Surprisingly, the entire process is less than 5 minutes, preferably less than 1 minute and most preferably between about 15 and 30 seconds. As the product exits the reactor, the product is at a temperature of between about 230 and 245xc2x0 F. under atmospheric conditions.
The product is passed through a cyclone that allows simple venting of the moisture and results in a dry product. The soy flour produced according to this process is bland with no beany, green or off-flavors and fully functional making it suitable for nutritional supplementation and use in food formulation.
The product is free flowing at all times. No slurry is formed and the high jacket temperatures maintain the water/steam in a volatile form to remove the flavors. Product is stable under conventional packaging, with no reformation of beany, off-flavors.
Soy flour treated in this manner retains functionality as demonstrated by preparation of soy milk in Example 2 and soy yogurt in Example 3. If significant denaturation of the soy proteins occurs, the protein will precipitate in milk or fail to coagulate in yogurt. Soy flour produced in the above manner preserves protein functionality while removing the beany flavor.
The product and method of the present invention are described in the following examples. These examples are provided as an illustration of the invention and are not intended to limit the invention.